This invention relates to thermoplastic molding compositions based on aromatic polyether sulfones and grafted, particulate diene rubbers produced by a special synthesis process, to a process for the production of the molding compositions by mixing of the components at elevated temperature and to their use for the production of moldings, primarily by injection molding.
Molding compositions of aromatic polyether sulfones are known. In general, they show very high heat resistance and excellent stability to chemicals but frequently do not achieve the high notched impact strength required for certain applications.
To improve notched impact strength, German Auslegeschrift 1,794,171 and U.S. Pat. Nos. 3,555,119 and 3,646,162 propose mixtures of polyether sulfones with impact modifiers consisting of styrene/acrylonitrile-grafted butadiene rubbers (ABS type). However, any improvement is obtained at the expense of a considerable reduction in the heat resistance of the molding compositions.
In addition to high notched impact strength, a sufficiently high level of weld line strength is required for many applications of polyether sulfone molding compounds, particularly in the automotive field. This is necessary for obtaining even relatively large injection-molded parts with several gate marks in a sufficiently high quality.
Although a level of toughness at room temperature and low temperatures sufficient for many applications of polyether sulfone molding compositions can be obtained with rubber modifiers of the ABS type, as described in German Auslegeschrift 1,794,171, U.S. Pat. Nos. 3,555,119 and 3,646,162, relatively large injection-molded parts show unfavorable mechanical properties because of inadequate weld line strength. It has now surprisingly been found that mixtures of aromatic polyether sulfones and grafted diene rubbers can be processed to molding compositions combining high heat resistance with high weld line strength by using grafted, particulate diene rubbers which have been grafted by a special process. The process according to the invention for the production of the graft polymers is characterized in that an initiator system of an organic hydroperoxide and ascorbic acid is used for the graft polymerization, giving a graft yield of more than 60% by weight.